Help - moderately urgent pre-trackday question - black gunk in air inlet manifold

[danielcwsmith]

I've just had my intake manifold off to replace a part between the throttle body and intake itself and noticed that there is black residue in each of the four intakes. I'll grab a photo asap, but I hadn't noticed it before and I'm setting off for Pembrey in a couple of hours for a trackday tomorrow. I'd rather not destroy and engine through ignoring an obvious sign.

 

It's an EU2 K series with a forward facing supersport intake.

 

TIA

[danielcwsmith]

This is the cleanest of the four:

This is the dirtiest:

[revilla]

It looks to me like oil residue and combustion products blown out of the crankcase breather into the inlet manifold with the blow by gasses. Do you drive it on track much? Do you drive it fairly aggressively otherwise? A lot of cars driven hard with throttle bodies would route the breather to a catch tank that would catch this sort of thing. On cars with standard plenum chamber and inlet manifold setups, it is routed to the inlet manifold for the engine to burn it for emissions reasons. The harder you push it, the more it will breathe. Also general wear to the cylinders and rings can result in more blow by gases. Unless it has suddenly increased it is probably just normal for your engine and usage. I don't think I'd cancel the track day for it.

[danielcwsmith]

I should add then that yes, I mainly track it, and also that the breathers from the top cover go to the dry sump bellhousing tank and a catch tank, so the route for the residue isn't immediately obvious. 

 

I'd not noticed it before, but that of course doesn't mean it wasn't there. The variation across the inlets had me wondering. It's a single 56mm throttle body as opposed to individual TBs, not that this should make a difference. There is a small hose from the fuel rail to the inlet manifold just behind the throttle body, so this is a potential source of "wet" substance I suppose.

 

I appreciate the view. I have to get petrol in a moment, so I shall drive it with ears wide open and a pounding heart I imagine!

[revilla]

Yes I saw your comments (on "another forum"  ) where you said that the breathers already route to a catch tank, so my comments are largely irrelevant in that case.

The "small hose from the fuel rail to the inlet manifold just behind the throttle body" really shouldn't provide a route for anything, that's e pressure reference for the fuel pressure regulator (to allow it to regulate fuel pressure at say 3 bar above manifold pressure, rather than atmospheric, as that's the differential pressure the injectors see).

You can / do (I believe) get reverse pulses in the gas flow in the inlet runners, from cam overlap and also from reflected pulses when the valves close, so it's possible that fuel may get carried back outward from the injectors into the manifold runners and if you have a bit of leakage around the valve stem oil seals this may carry a bit of oil back with it.

Is the engine burning much oil? I guess it puts some out to the catch tank but does it burn noticeably more than it breathes out?

[danielcwsmith]

Another *cough* forum. Yes. 

The engine actually uses very little oil. Most of the catch tank is thin condensation, but the oil pressure isn't low or lowering slowly over time, nor is the exhaust smokey. Granted I don't have a dipstick, but all seems well.

I think I'll make a dipstick up for the drysump and check before each outing to see if there are losses, because they'll start small I guess, but grow and I'd rather catch an issue early. It seemed odd that the inlets were variably affected, but I guess that would point to wear on individual cylinders and associated gubbins as opposed to ingress from the throttle-body end.

All input much appeciated so far.